Many situations exist in which it is important to have rapid, reliable, inexpensive tests that can be run by untrained individuals in the field, home, or other non-laboratory setting. Immunoassays have many of these characteristics. One type of immunoassay, referred to as an immunochromatographic or lateral flow strip test, has been successfully developed into ‘one-step’ tests and employed for on-site analysis. The over-the-counter home pregnancy test is an example of a simple, one-step immunochromatographic strip test.
Immunoassays have been used to detect substances in many different kinds of samples in many different markets, including the agriculture market. Modern biotechnology methods are being used to genetically modify plants. These genetically modified plants, and the seeds, grain and food derived from them all may contain novel or recombinant proteins. It is important to determine the presence of such proteins for regulatory, environmental, safety, and world trade issues. Very large amounts of grain and seed are harvested, transported, mixed, stored, distributed and traded throughout the world, and it is important to have tests that can detect these novel proteins in order to address these issues. It is desirable to have a rapid, simple and inexpensive method that can be used to test grain samples at many points along the distribution channel including trucks, elevators, barges, ships, etc. A strip test is ideally suited for this purpose. For example, recently, an immunochromatographic strip test (strip test or lateral flow device, LFD) that detects a specific protein in genetically modified soybeans was developed.
Strip tests are comprised of multiple porous components, membranes and filters, through which liquid sample is drawn by capillary action. Analyte in the sample reacts with the test reagents contained within the test strip as it traverses the length of the strip. To detect an analyte (such as a protein or mycotoxin) in grain or seed (e.g., corn, soybean, rice, wheat, etc.), it is necessary to grind the grain into a powder and then extract the protein from the powder with a liquid that is then separated from the solid material and assayed using the test. To achieve the highest sensitivity test possible, it is important to extract as much of the analyte from the grain as feasible. This requires that the grain be ground to a fine powder to facilitate efficient extraction. However, very fine particulate matter suspended in the liquid sample clogs the pores of the strip test components causing the strip to run slowly, erratically or not at all. Additional steps or test components employed to remove the particulates only serve to complicate the testing process and increase the cost of the test and time-to-result.
What is needed is a means for preparing and testing a finely ground powdered sample that maximizes extraction efficiency, sensitivity, speed and reliability of the strip test while minimizing the complexity and cost.